1. Field of the Invention
The present invention relates to an optical crossconnect that uses an optical switch to set optical signal paths, an optical network device, and a connection status supervisory method. More particularly, the present invention relates to an optical crossconnect capable of supervising optical signal paths set in the optical crossconnect without affecting the service signal, an optical network device, and a connection status supervisory method.
2. Description of the Related Art
An optical crossconnect system, which uses an optical switch, can process a large number of optical signals because it can switch signals regardless of their formats. The introduction of Wavelength-Division Multiplexing (WDM) technology allows the optical crossconnect to process and switch an even larger number of optical signals. Because this technology makes signal-path setting easier and protection more efficient, much effort has been made at the research and development of this field. This is described in detail, for example, in xe2x80x9cExamining an integrated solution to optical transport networking.xe2x80x9d, Wavelength Division Multiplexing: (The first ever European meeting place for WDM Systems, Network, Marketing and Engineering Professionals), pp. 18-23, November 1997, London.
Conventionally, several methods for supervising optical paths in an optical crossconnect have been studied. For example, the supervisory signal is superimposed over the service signal. This method is described, for example, in xe2x80x9cA study of the method for supervising optical paths using the pilot tone signal in an optical path networkxe2x80x9d by Hamazumi et. al., pp. 45-52, in Technical Report of IEICE, OCS96-66 or in xe2x80x9cInter-Network interface for photonic transport networks and SDH transport networkxe2x80x9d by Satoru Okamoto et. al., pp. 850-855, in GLOBECOM""97 paperS24.1, Phoenix Ariz. November 1997.
Conventionally, the supervision of the optical paths of an optical crossconnect has been done in one of the methods described below. In the first method, the input signal of the optical crossconnect is modulated, and the power of this signal is supervised at the output of the optical crossconnect. When the magnitude of the signal is abnormal, the corresponding optical path is assumed to be abnormal. In the second method, the power of the input signal of the optical crossconnect is compared with that of the output signal. When the optical power has been attenuated significantly, the corresponding optical path is assumed to be abnormal.
However, in the optical crossconnect in accordance with the first method, the input signal is modulated and therefore the optical signal output from the optical crossconnect is also modulated. This modulation affects the quality of the optical signal.
In the optical crossconnect in accordance with the second method, the loss of the optical switch can be supervised but the service signal cannot be identified. Therefore, this method is not appropriate for supervising whether or not the optical paths are normal.
The present invention seeks to solve the problems associated with the prior art described above. It is an object of the present invention to provide an optical crossconnect, an optical network device, and a connection status supervisory method that can supervise, without affecting the service signal, the optical signal paths that are set in the optical crossconnect.
The optical crossconnect according to the present invention is an optical crossconnect selectively connecting at least one input terminal with at least one output terminal, the optical crossconnect comprising an optical switch connecting at least one input port connected to the at least one input terminal with at least one output port connected to the at least one output terminal; at least one supervisory light generating circuit for sending a supervisory light from each of the at least one output port to the optical switch; and at least one supervisory light receiving circuit for receiving the supervisory light output from the at least one input port.
An optical network device according to the present invention is an optical network device transferring optical signals among a plurality of optical node devices interconnected via optical transmission lines, wherein each of the plurality of optical node devices comprises the optical crossconnect described above.
A connection status supervisory method according to the present invention is a connection status supervisory method for supervising a connection status of an optical crossconnect, the connection status supervisory method comprising the steps of generating a supervisory light to supply it to each of output ports of the optical crossconnect, the supervisory light being superimposed over by a signal that is unique; receiving the supervisory light output from each of input ports of the optical crossconnect; and determining whether or not an optical path is normal by referencing the signal superimposed over the supervisory light received in the step of receiving the supervisory light.